Pigment concentrates are prepared by breaking down pigments with the aid of shear machines in a liquid carrier medium and dispersing them so finely that the pigment is permanently in the form of the primary particles. Suitable shear machines are known to the skilled worker and are described with particular attention to American technologies in, for example
C.H. Hare, Protective Coatings--Fundamentals of Chemistry and Composition, Technology Publishing Comp., Pittsburg (1994). PA1 H. Kittel, Lehrbuch der Lacke und Beschichtungen, Vol. III, p. 239 ff., Verl. W. A. Colomb, Berlin, Oberschwandorf (1976) PA1 J.V. Robinson, R. N. Thompson, Dispersants, in Paper Coating Additives, Monograph No. 25, TAPPI, Atlanta 1963 PA1 J. D. Schofield, Polymeric Dispersants, in Handbook of Co a ting Additives, L. J. Calbo (Ed.) Vol. 2, Marcel Dekker, New York, Basel, Hong Kong (1992). PA1 C. Baumann, D. Feustel, U. Held, R. Hofer, "Stabilisierungssysteme fur die Herstellung von Polymer-Dispersionen" [Stabilizing Systems for Preparing Polymer Dispersions] in: Welt der Farben, p. 15ff., (2/1996). PA1 the radicals R.sup.1 and R.sup.2 independently of one another are alkyl groups having 1 to 36 carbon atoms or hydrogen, PA1 the radicals R.sup.3 and R.sup.5 independently of one another are alkyl groups having 1 to 36 carbon atoms or hydrogen, PA1 the radical R.sup.4 is a straight-chain or branched alkylene group having 2 to 12 carbon atoms or a group (--CH.sub.2 --CHR.sup.6 --O).sub.z, PA1 the radical R.sup.6 is hydrogen or a methyl group, PA1 the radicals R.sup.7 and R.sup.8 independently of one another are alkyl groups having 1 to 36 carbon atoms or hydrogen, PA1 the indices x and y independently of one another are numbers in the range from 1 to 200, PA1 the index z is a number in the range from 1 to 20, and PA1 the index n is a number in the range from 2 to 12, PA1 radicals R.sup.1 and R.sup.2 must not both simultaneously be hydrogen, PA1 the sum of the carbon atoms in the radicals R.sup.1 and R.sup.2 is in the range from 6 to 38, PA1 radicals R.sup.3 and R.sup.5 must not both simultaneously be hydrogen, PA1 the sum of the carbon atoms in the radicals R.sup.3 and R.sup.5 is in the range from 6 to 38, PA1 the sum (x+y) is a number in the range from 5 to 200. PA1 the radicals R.sup.1 and R.sup.2 and, respectively, R.sup.3 and R5 are alkyl groups having 12 to 18 carbon atoms, and PA1 the sum (x+y) is a number in the range from 5 to 120. PA1 a) from 10 to 80% by weight of one or more pigments, PA1 b) from 0.1 to 20% by weight of one or more diol alkoxylates from the group of compounds of the formulae (I) to (III) ##STR3## PA1 in which PA1 with the further proviso that PA1 c) from 15 to 85% by weight of a liquid carrier medium.
Owing to the importance of dispersing for the varnish, paint and printing ink industry, both the dispersing process and the low and higher molecular mass compounds suitable for stabilizing the primary particles are described at length in the technical literature. By way of example, reference may be made here to:
From the known prior art it is not possible to derive any teaching relating to the targeted selection of additives which effectively support the formulation of pigment concentrates, especially when these pigment concentrates are intended to allow the preparation of low-emissions or emissions-free paints and printing inks or when they are to be free from environmentally or ecotoxicologically unacceptable substances.
A particular difficulty is represented by the formulation of aqueous pigment concentrates, especially when these concentrates are to be formulated without the addition of low molecular mass cosolvents such as ethylene glycol or propylene glycol. Thus, as the skilled worker is aware, so-called pigment dispersants based on polyphosphates or polyacrylates, although outstandingly suitable for maintaining pigments and fillers in suspension alongside the emulsifier-stabilized or protective-colloid-stabilized latex particles in emulsion paints, are unsuitable for preparing pigment concentrates having the profile of requirements described above.
The majority of dispersants, which are of outstanding suitability in organic carrier oils of different polarities, fail if water is chosen as the continuous phase for the pigment concentrates. Surfactant-type dispersants which provide good pigment wetting, such as alkylphenol polyglycol ethers--see, for instance, patent GB 861 223--in turn have come under environmental debate in recent times in respect of their biodegradability, both in the laundry detergent and cleaning products industries, where they have already been fully replaced as surfactants in Germany, and in emulsion polymerization, i.e., in the production of aqueous binders for emulsion paints; in this context see:
A further difficulty in respect of selecting additives to formulate pigment concentrates is that the dispersing additive must be selected such that, substantially independently of the carrier oil, the viscosity of the continuous phase decreases as the shear force increases; i.e., the dispersion must possess pseudoplasticity and must in no case be dilatant.
When formulating pigment concentrates care must further be taken to establish a special balance between water retention capacity and hygroscopy such that the intrinsic drying of the concentrate is greatly retarded. Partially dried pigment concentrates should be readily redispersible. On the other hand, water retention capacity and hygroscopy must not be so high that the finished coating becomes sensitive to water.
Other service properties of the finished paint as well, such as freeze/thaw stability, storage stability, and shear stability, must not be adversely affected, with the same applying to properties of the cured film, e.g., clarity, gloss, or resistance to blushing.
A further particular requirement to be met by the pigment concentrates to be developed in accordance with the invention is that there must be compatibility with a broad spectrum of binders, organic and inorganic pigments, which in turn are usually present dispersed in what are known as base coats, and at the same time both with water and with the different solvents used in paints, and also with the highly alkaline waterglasses used in silicate paints.
A high percentage of liquid paints are produced industrially by preparing the polymeric binder in a separate stage and then blending it with the other ingredients to form the finished paint. If coloration is to take place at this point rather than later, the pigment is dispersed with the binder in an upstream stage in a high-speed mixer or in a dissolver, and is then diluted down to use concentration. Of particular interest in connection with this invention are architectural paints for home improvement use and for the craft sector, both for interior and exterior coatings. The binders for these paints are prepared by emulsion polymerization in aqueous phase. In practice, the aqueous phase frequently comprises volatile organic solvents, known as coalescents, which are added either during the polymerization or later and which assist in film formation by partially dissolving the latex particles and also promote leveling. The inherent odor of these coalescents, especially that of the known and widespread 2,2,4-trimethyl-3-hydroxypentyl isobutyrate (Texanol.RTM.), can be perceived for several days in freshly painted rooms. In modern-day society, however, this odor is increasingly found to be a nuisance. There is therefore interest in keeping modern paints totally free from such coalescents and other volatile solvents or cosolvents and in also not introducing such ingredients via the pigment concentrates either.
Besides the coloring of paints during production, a significant percentage are not colored until immediately before their use, whether in order to establish special shades or for the purpose of meeting particular customer wishes. In these cases, an industrially premanufactured pigment concentrate is admixed to a white or pastel stock paint. This near customer form of color adjustment can be done either by tradespersons or on a semi-industrial or industrial basis. In these cases the pigment concentrate is usually admixed in a proportion of from 5 to 200 ml per l of stock paint. Often, a combination of two or three different pigment pastes is required in order to arrive at the desired shade. The pigment concentrates commonly comprise high pigment concentrations; i.e., the pigment volume concentration--abbreviated to pvc--is normally between 10 and 80%.
DE-A-26 28 145 discloses adducts of ethylene oxide on specific glycols, containing a --C.ident.C-- group as structural element. These compounds are said to be suitable as moisteners, dispersants, nonionic antifoams, and viscosity stabilizers, and to develop their action in aqueous solution at a lower concentration than in the case of conventional surfactants. Other than listing the abovementioned areas of application, however, DE-A-26 28 145 does not disclose any specific further details or exemplary embodiments.
EP 565 709 Bl discloses aqueous inkjet inks which include polyol-alkylene oxide condensates as a cosolvent. According to page 4, lines 9-15 of this document, the polyol contains in particular three or more OH groups. There is explicit mention of specific triols such as glycerol, trimethylolpropane, trimethylolethane, 1,2,4-butanetriol, and 1,2,6-hexanetriol, and also of pentaerythritol and di(trimethylolpropane) as tetrols, glucose as a pentol, and sorbitol and inositol as hexols. The use of diols, however, is said to be fairly unsatisfactory. It is found in this context that alkylene oxide condensates of diols are generally not compatible with pigment dispersions, with the possible exception of neopentyl glycol alkoxylates.
WO 96/7689 discloses copolymers of the general formula (A--COO).sub.2 --B, in which A has a molar weight of at least 500 and is the residue of an oil-soluble complex monocarboxylic acid of specific structure and B has a molar weight of at least 500 and is the divalent radical of an alkyl glycol or of a polyalkylene glycol. The copolymers of WO 96/7689 are said to be suitable for dispersing inorganic pigments in organic media.
EP 735 109 A2 discloses aqueous pigment preparations containing inter alia from 10 to 80% of a pigment and from 0.1 to 20% of an alkoxylation product obtained by adding optionally substituted styrenes onto optionally substituted phenols and reacting the adducts with ethylene oxide and/or propylene oxide.
DE 39 20 130 A1 discloses the use of partial esters of oligoglycerols with fatty acids as pigment dispersants for aqueous paint dispersions. Said partial esters can if desired have been ethoxylated and/or propoxylated.
The present invention was based on the object of providing effective additives for preparing pigment concentrates, and the pigment concentrates thereby obtainable themselves, which meet the large number of abovementioned criteria relating to the desirable profile of properties of such additives and, respectively, of the pigment concentrates themselves.